<!DOCTYPE html>
<html lang='en'>
<head>
    <meta charset='UTF-8'>
    <title>包装类</title>
</head>
<body>
    <script>
        let a = new Number(123);
        console.log(a);  // Number {123}
        console.log(typeof a);

        let b = new String('慕课网');
        console.log(b);  // String {'慕课网'}
        let c = new Boolean(true);
        console.log(c);  // Boolean {true}

        let d = 456;
        console.log(d.__proto__ === Number.prototype);  // true

        console.log(d + a);  // 579
    </script>
</body>
</html>
